add build option debug-disk-pool to log disk buffers allocated by category #2969

Job	Run time
Simulations	17m 41s
MingW (address-model=64)	15m 56s
Build (asio-debugging=on picker-debugging=on windows-version=vista)	11m 13s
Test (address-model=32 crypto=built-in)	16m 46s
Build (deprecated-functions=off)	11m 16s
Test (address-model=64)	13m 48s
Test (release)	17m 34s
	1h 44m 14s

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